Evidence Heavy Caffeine Drinkers Exhibit Caffeine Tolerance

Caffeine is a drug widely used throughout the world, mostly in drinks. Physiological effects from the intake of caffeine include: changes in heart rate (HR), blood pressure (MAP) and respiration rates (RR). With consistent consumption of caffeine, these effects may be dampened. Different caffeine vectors affect the rate of absorption into the body (perhaps due to the other substances in the drinks in addition to the caffeine). This study investigated the effects of consuming pure liquid caffeine (Kafin8®) caffeine on HR, BP and RR of heavy caffeine drinkers and those who do not consume caffeine. HR, MAP, and RR were measured before caffeine administration, one, five, and ten minutes after ingestion of 300mg of liquid caffeine. In this COVID-19 attenuated study (N=1 for each group), the regular caffeine consuming subject had a lesser increase in HR (9.1 % over 10 min) than the subject who normally refrained from caffeine consumption (22 % over 10 min.); similarly, MAP increased more in the subject who did not consume caffeine on a regular basis, (9.3 % over 10 min.) than the subject who consumed caffeine on a regular basis (2.2 % over 10 min.). However, no change was seen in RR for any subject. Although the study was interrupted by COVID-19, the data supported the hypothesis that physiological responses to caffeine consumption were reduced in those who consume caffeine regularly; thus caffeine tolerance is demonstrated.